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Effect of Dissolution Treatment on Standard and Soil Clays¹

ABSTRACT

Alkaline dissolution methods and iron removal treatments for solubilization and extraction of amorphous components were evaluated as to their effects on the crystalline clay mineral components of amorphous-crystalline clay mixtures. The procedure involved sequential treatments of sodium dithionitecitrate-bicarbonate for iron oxide removal and boiling 0.5N base for solubilization of amorphous alumina, silica, and alumino-silicate. Higher weight losses were obtained with NaOH than with KOH dissolution for the majority of clay samples. The CEC of kaolinite, halloysite, interstratified mica-chlorite, and chlorite did not change substantially after NaOH or KOH dissolution. The CEC of nontronite decreased from 86 to 19 meq/100 g after KOH dissolution but only decreased to 68 after NaOH dissolution. In contrast, the CEC for biotite increased from 15 to 35 meq/100 g after NaOH treatment and only increased to 21 meq/100 g after KOH treatment. Crystal structure of clay minerals was altered more markedly with NaOH treatment than with KOH. Extract analyses for Si, Al, and Fe indicated the progressive amounts of solubilization and extraction for each step of the sequential treatments employed. Use of acid ammonium oxalate in place of sodium dithionite-citrate-bicarbonate greatly reduced struetural alteration of crystalline clays without an appreciable decrease in the efficiency of removal of amorphous constituents.

¹ Technical Paper no. 2903, Oregon Agr. Exp. Sta., Corvallis. Financial support through National Science Foundation Grant GA-1355 is gratefully acknowledged. Presented before Div. S-9 Soil Science Society of America, Nov. 10, 1969. Detroit, Mich.

² Research Assistant and Professor, respectively, Department of Soils, Oregon State Univ.

Received for publication June 11, 1970. Accepted for publication November 3, 1970.